Biomechanical Comparison of a Transosseous-Equivalent All-Knotless Rotator Cuff Repair versus Traditional Double-Row Repair
Introduction: Currently controversy remains as to which arthroscopic techniques are superior regarding strength of repair, surgical time, healing, and clinical results. The purpose of this study was to perform a biomechanical comparison of a traditional tied double-row construct utilizing a horizontal mattress technique for the medial row versus a transosseous-equivalent all-knotless (TEAK) construct utilizing a load-sharing suture technique for the medial row. Methods: Rotator cuff repairs were performed on shoulders from five matched porcine pairs randomly assigned to either a traditional tied double-row repair technique or a TEAK repair construct. The constructs were tested in tension up to 3,000 cycles, then loaded at 2mm/sec until failure and biomechanical differences between constructs were determined by paired t-tests. Results: There were no statistically significant biomechanical differences between the traditional tied and TEAK repairs. 2 traditional tied repairs failed during cycling; the remaining 3 failed through tearing at the suture-tendon interface; 3 of the all-knotless repairs failed through sutures pulling through the bone anchor and 2 failed by sutures tearing at the suture-tendon interface. Discussion: In a porcine rotator cuff model, the TEAK construct was biomechanically comparable to a traditional tied double row repair. Level of Evidence: Experimental study. Keywords: Rotator cuff tear; Arthroscopy; Knotless suture rotator cuff repair.
The rotator cuff functions to dynamically stabilize the glenohumeral joint and allow for humeral range of motion in multiple planes. Rotator cuff tear etiology follows a bimodal age distribution; younger individuals typically experience injuries with overhead throwing activities, while elderly patients suffer from chronic degenerative tears. Orthopaedic literature has speculated that repetitive microtrauma secondary to eccentric traction forces at the supraspinatus and infraspinatus tendons during the latter stages of the overhead throwing motion contributes to articular-sided rotator cuff tears . Shear stresses at the articular aspect of the cuff are maximized when the arm is rotated into an abducted and externally rotated position, and these forces consequently contribute to rotator cuff tears . Operative management of rotator cuff tears includes open, mini-open, and arthroscopic procedures; however, currently the trend amongst most orthopaedic surgeons today favors arthroscopic cuff repairs. Arthroscopy permits cuff repair with less dissection of the surrounding soft-tissue, has a lower incidence of developing fibrous adhesions and allows for earlier postoperative range of motion exercises [3-6]. A common complication is structural failure of the cuff repair, upwards of 90% in certain published studies. This has been attributed in part to an inadequately restored anatomical footprint, consequently hindering bone-to-tendon healing [4,7-12]. Other factors contributing to rotator cuff repair failure include suture anchor loosening, suture failure, knot loosening, failure at the suture-tendon interface, and fatty degeneration or muscular atrophy of the cuff [4,8,9-11,13-15]. Orthopedic literature has shifted focus toward studies of arthroscopic repair techniques aimed at providing stability with cyclic loading, minimizing gap formation, and restoration of the anatomical footprint . Primary concerns with rotator cuff repair include biomechanical stability (gap formation, construct stiffness, cycles to failure, load to failure, and ultimate tensile strength) and fixation offered by single-row versus double-row repair [4,15,16]. Reapproximating the rotator cuff footprint theoretically allows for greater surface area of contact between the tendon and bone, which improves force distribution and healing potential [3,4,11,13,16-18]. Other techniques utilized in rotator cuff repair include the transosseous method (soft-tissue fixation with sutures placed into transosseous tunnels) utilized in open and miniopen techniques and the arthroscopic transosseous-equivalent (TE) method . TE suture bridge techniques include knotless and traditional knot-tying approaches. It is theorized that the combination of a knotless construct with a medial load sharing technique offers greater tissue holding, an inherent rip stop which prevents tendon pullout, and theoretically reduced likelihood of medial row tissue strangulation which consequently may lower retear rates . While there exist numerous biomechanical studies in the literature comparing various constructs for rotator cuff tear repairs, controversy remains as to which arthroscopic techniques are superior regarding strength of repair, surgical time, ultimate healing, and final clinical results. The purpose of this study was to perform a biomechanical comparison of a traditional double-row construct utilizing a horizontal mattress technique for the medial row versus a TE all-knotless (TEAK) construct utilizing a load-sharing suture technique for the medial row. The null hypothesis was that there will be no significant differences in repair site gapping, stiffness, or ultimate load to failure between the 2 constructs. MATERIALS & METHODS Study Design A power analysis based on a pilot study of 2 fresh-frozen porcine shoulder pairs indicated that 5 matched pairs would be sufficient to detect a difference in constructs at 80% and alpha of 0.05. 5 matched porcine shoulder pairs were dissected down to the humerus and posterior superior rotator cuff with removal of the scapula and additional soft tissue. The infraspinatus muscle and tendon was identified on each specimen, after which the remaining soft tissues were carefully dissected off of their attachment on the humerus. The infraspinatus tendon attachment was sharply dissected completely from its insertion at the greater tuberosity to mimic a full-thickness retracted rotator cuff tear. For a pairwise comparison, right and left shoulders were randomly assigned to either the traditional tied double-row repair technique or the TEAK repair construct. Suture Techniques The traditional tied double-row construct utilized four 4.5mm single-loaded suture anchors with 2 horizontal mattress knots tied at the medial row and 2 vertical mattress knots in the lateral row. The medial row anchors were placed 8mm medial to the tendon edge with the suture placed 10mm medial to the tendon edge. The lateral row anchors were placed 8mm lateral to the tendon edge and tied in a vertical fashion with one limb passing around the medial row horizontal mattress knot. A 1cm distance was kept between the medial and lateral anchors in the anteroposterior direction (Figure 1A, Figure 2A). The TEAK construct is composed of four suture anchors per repair, 2 double-loaded Healix Advance 4.5mm anchors (Mitek Sports Medicine, Raynham, MA) for the medial row and two knotless Healix Advance 4.75mm anchors in the lateral row. One of the suture anchors was placed 8 mm medial to the tendon insertion site, and one of the sutures from the double-loaded anchor was removed and used to create an inverted horizontal mattress suture placed approximately 10mm from the tendon edge to function as a rip-stop. The two tails from the remaining suture within the medial anchor were placed medial to the inverted mattress technique suture in a narrow horizontal pattern and left untied. All four of the suture tails were then placed within the 4.75mm anchor and secured with appropriate tension 8mm lateral to the lateral border of the tendon insertion site. This process was repeated in the same fashion, keeping a 1cm distance between the medial and lateral anchors (Figure 1B, Figure 2B).
Results of the biomechanical analysis of cyclic and failure testing are presented in Table 1, with means (standard deviation), P-values, and post-hoc power achieved for each test parameter. Cyclic testing of the traditional tied double-row repair and all-knotless constructs showed no statistically significant differences in repair gap length, total construct displacement, initial stiffness, or final cycle stiffness. Three of the five traditional tied constructs survived the 3,000-cycle protocol; of the two that did not, one failed at 37 cycles and the other at 47 cycles, both at the suture-tendon interface by the sutures tearing through the infraspinatus tendon. All 5 of the TE all-knotless constructs survived the 3,000 cycles of cyclic testing.